As processes for the anticorrosive treatment of metallic members of frame-work and structures, there have been employed rubber lining process, resin lining process and organic or inorganic coating process. Processes for the resin lining which have been employed particularly popularly are as shown below:
(1) Cold-curing FRP lining with a liquid resin:
An article to be treated such as a metallic member of frame-work is lined by means of the lamination with a glass fiber base impregnated with (a) a liquid resin composition obtained by dissolving an unsaturated polyester resin in a vinyl monomer such as styrene and incorporating a peroxide which is decomposed at ambient temperature such as methyl ethyl ketone peroxide (MEK PO) therein as hardening agent, (b) a composition obtained by dissolving epoxy(metha)acrylate resin (vinyl ester resin) in a vinyl monomer such as styrene and incorporating MED.PO therein as hardening agent or (c) a liquid resin composition comprising a liquid epoxy resin and an amine cold-setting hardening agent such as a primary or tertiary amine, and then it is cured at ambient temperature.
This process has the following problems: Working time is limited within a short period of time, since the cold-setting resin composition is used. Working environment is bad, since the liquid resin and monomer are used for the impregnation molding. The composition is not uniform, the lining thickness is uneven and quality of the lining material is unstable, since the weighing and mixing are effected in situ and the lamination is effected by coating by hand.
(2) Lining process by coating with liquid resin:
As the liquid resin lining processes, there may be mentioned a process wherein a liquid resin such as the above described cold-setting unsaturated polyester resin, vinyl ester resin, epoxy resin or urethane resin is applied to an article by means of a brush or by spraying: and a process wherein a liquid resin composition comprising an ultraviolet-curing resin such as an unsaturated polyester resin, vinyl ester resin or urethane acrylate incorporated with a vinyl monomer, photosensitizer, pigment, etc. is applied to an article by means of a brush or by spraying and then the coating film is cured by means of an ultraviolet irradiation device. However, the coating films obtained by these processes are thin. Their thickness is about 10-200.mu.. Their anticorrosive effect does not last for a long period of time. The coating films are not highly resistant to a shock caused by an external force. By these processes, it is quite difficult to form a thick coating film having a high durability.
(3) Lining process by coating with thermosetting prepreg sheet:
An article to be treated is lined with a solid prepreg sheet obtained by impregnating a fibrous base with a liuquid composition comprising a solid or semi-solid, unsaturated polyester resin, vinyl ester resin or epoxy resin added with suitable amounts of a diluting agent, a heat-active latent curing agent and a solvent and removing the solvent by drying or with a solid prepreg sheet (generally called SMC) obtained by impregnating a glass fiber base with a liquid composition comprising an unsaturated polyester resin containing terminal or side chain COOH groups or vinyl ester resin added with a vinyl monomer, MgO, a heat-active organic peroxide and calcium carbonate or another filler, and then the sheet is cured by hot air, infrared rays or a hot press.
However, such a thermosetting prepreg sheet is not cured unless it is heated and, therefore, the application thereof to an article of a high heat capacity such as a large tank, pipe or structure is difficult. Further, it must be kept at a low temperature during the storage, since it is gradually cured even at ambient temperature during the storage for a long period of time.
Thus, the conventional resin linings have many problems due to properties of the resins used. Under the circumstances as above, a resin composition suitable for the use as lining and free from the above problems has been demanded. Further, the development of a prepreg sheet containing such a resin composition and suitable for lining has also been demanded.
As coating materials for preventing metals from corrosion, there have been used tapes and sheets comprising woven or non-woven fabrics of synthetic fibers or glass fibers impregnated with petrolatum.
The petrolatum coating materials have been used broadly, since they are not cured or decomposed during the storage for a long period of time.
The petrolatum anticorrosive tapes are not cured or decomposed with time and their anticorrosive properties are maintained for a long period of time. However, the petrolatum is a soft, clay-like substance and, therefore, it is not resistant to an external force or shock. It cannot be used as it is when it is to be contacted with other substances or when it is applied to, for example, an article to be placed under the ground such as a buried pipe. In such a case, it has been required to protect the same with polyethylene tapes or gum tapes. Further, since the petrolatum is adhered to a metal merely by its adhesive force and it is soft, the petrolatum has a defect that it cannot be applied to an article which will be subjected to the vibration or dynamic action. In addition, petrolatum has a low melting point and a poor thermal resistance and it could not be used at a temperature above 70.degree. l C. in general. There has been proposed an idea that the outer surface of the petrolatum coating material is coated with a cold-setting coating material or thermosetting coating material for overcoming the above defects. However, this idea also has serious defects of workability that the cold-setting coating material is sticky and that the thermosetting coating material requires a heat treatment. Another defect of those coating materials of curing type is that they require a long curing period of time and, therefore, if it rains during the operation, the working becomes impossible. Under the circumstances as above, the development of an anticorrosive petrolatum coating material for metals which can be treated easily and which has a high anticorrosive capacity has been demanded.
For the prevention of corrosion of steel structures such as pipe lines for transporting petroleum from a tanker, the following various structures have been proposed: (1) A steel structure in which the steel is directly coated with a synthetic resin: This process is effected by extruding a molten thermoplastic resin such as polyethylene resin on the steel surface to coat the latter. However, the coating film is easily broken when the steel is cut and rust is formed rapidly at the broken part. (2) A steel structure the surface of which is coated with plural coating films: This is obtained by applying a paint repeatedly at time intervals to the steel surface, since if the paint is applied thereto at once to form a thick coating film, the coating film surface contracts. However, the resulting coating layer has poor physical properties such as impact resistance and cutting resistance and, therefore, the steel surface is hurted, since the coating layer does not contain any reinforcing material such as fibers. (3) A steel structure obtained by laminating a sheet of a thermosetting fibrous reinforced plastic (hereinafter referred to as FRP) such as SMC (sheet molding compound) sheet in B-stage (semi-cured) and curing the FRP sheet. This structure has the following defects: If the FRP sheet in its B-stage is allowed to thermoset without using a mold fit for a shape of the steel, bubbles contained in the FRP sheet are expanded during the thermal polymerization of the resin to form pin holes. A protective layer of a uniform thickness cannot be formed on the steel surface, since the resin is fluidized by heat. Consequently, the anticorrosive properties of the layer is unsatisfactory. The use of the mold makes the operation complicated. (4) A structure comprising a steel on the surface of which is laminated and FRP protective layer by so-called hand lay-up lamination technique: In this structure, it is difficult to penetrate a resin in the fibers in such a manner that bubbles are not incorporated therein. Consequently, pin holes are formed, and the anticorrosive properties are poor. As described above, a structure having satisfactory anticorrosive properties could not be obtained in the prior art, though various anticorrosive structures have been proposed. Under the circumstances as above, it has been demanded to develop an anticorrosive coating material for metals having excellent anticorrosive properties such as durability, impact resistance, cutting resistance and rust preventive properties.